I. Field
The following description relates generally to wireless communications, and more particularly to signaling decoding statuses in a wireless communication system that employs uplink multiple-input multiple-output (MIMO).
II. Background
Wireless communication systems are widely deployed to provide various types of communication content such as, for example, voice, data, and so on. Typical wireless communication systems can be multiple-access systems capable of supporting communication with multiple users by sharing available system resources (e.g., bandwidth, transmit power, . . . ). Examples of such multiple-access systems can include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, orthogonal frequency division multiple access (OFDMA) systems, and the like. Additionally, the systems can conform to specifications such as third generation partnership project (3GPP), 3GPP long term evolution (LTE), ultra mobile broadband (UMB), multi-carrier wireless specifications such as evolution data optimized (EV-DO), one or more revisions thereof, etc.
Generally, wireless multiple-access communication systems can simultaneously support communication for multiple user equipments (UEs). Each UE can communicate with one or more base stations via transmissions on forward and reverse links. The forward link (or downlink) refers to the communication link from base stations to UEs, and the reverse link (or uplink) refers to the communication link from UEs to base stations. Further, communications between UEs and base stations can be established via single-input single-output (SISO) systems, multiple-input single-output (MISO), multiple-input multiple-output (MIMO) systems, and so forth. In addition, UEs can communicate with other UEs (and/or base stations with other base stations) in peer-to-peer wireless network configurations.
Conventionally, a UE can transmit a single codeword to a base station over the uplink (e.g., at a given time, . . . ). For instance, the base station can receive and attempt to decode the single codeword. If the single codeword is successfully decoded, then the base station can signal an acknowledgment (ACK) to the UE. Alternatively, if the single codeword fails to be successfully decoded, then the base station can signal a negative acknowledgment (NAK) to the UE. For example, a one bit indicator can specify a decoding status (e.g., an ACK or a NAK, . . . ) to the UE for the single codeword (e.g., “1” can indicate an ACK and “0” can indicate a NAK, “0” can indicate an ACK and “1” can indicate a NAK, . . . ). The one bit indicator can be a Hybrid Automatic Repeat Request (HARQ) indicator. Further, the indicator can be carried on a Physical HARQ Indicator Channel (PHICH).
Typically, a one bit indicator can be carried on a PHICH to identify a decoding status of a single codeword corresponding to a single transport block sent on an uplink data channel (e.g., Physical Uplink Shared Channel (PUSCH), . . . ). However, conventional use of a one bit indicator carried on a PHICH can cause ambiguity when more than one codeword is sent on an uplink data channel (e.g., PUSCH, . . . ) by the UE to the base station. For instance, multiple codeword transmissions in the uplink can be supported to extend uplink peak rates by implementing uplink MIMO. Yet, attempting to signify more than one decoding status corresponding to more than one codeword to the UE via a one bit indicator carried on a PHICH can cause ambiguity (e.g., a NAK can be sent when one codeword fails to be successfully decoded or when more than one codeword fails to be successfully decoded, . . . ). Accordingly, the UE may be unable to unambiguously recognize whether the multiple codewords are successfully decoded, unsuccessfully decoded, or a subset of the multiple codewords are successfully decoded with a remainder of the multiple codewords being unsuccessfully decoded. For instance, the foregoing can lead to unnecessary retransmission of codeword(s) that are successfully decoded by the base station, which can cause inefficiency in the wireless communication environment.